As a conventional device of this type, the present applicant has filed a patent application (matured into JP-A-7-25578) concerning a dismounting device for a heavy load hoisting member, in which top wires are provided between a base and a hook of a crane, bottom wires having foundation ends mounted on the base are engaged with wire engagement portions of a heavy load, respectively, and rings at ends of the bottom wires are fitted into a mast erected on the base. In this device, the base includes a pair of plates each formed into an approximate rectangle, a pair of side plates arranged at both margins of the plates to connect these plates at a predetermined interval, and a bottom block arranged at the bottom margin center of the paired plates. The paired plates are formed with, at centers thereof, T-shaped holes in an opposing manner, respectively, and the mast is erected on the bottom block to protrude into the T-shaped holes.
Slidably fitted onto the mast is a slider having a front end to be pushed up by a first resilient body under loadless state so that the front end fits the top of the mast, and slider lowering means is configured to lower the slider by overcoming a resilient force of the first resilient body. Further, locking means is configured to temporarily lock the slider in a lowered state of the slider, and unlocking means is configured to unlock the locked slider. Moreover, the slider lowering means includes a sensor rod which is vertically movably inserted into the base, whose bottom protrudes downward from the bottom of the base, and which is connected to the slider via tension member.
In the thus configured dismounting device, the base is firstly suspended by the hook of the crane through the top wires, and this base is lowered onto an upper surface of a heavy load or onto a ground close to the heavy load, so that the sensor rod downwardly protruded from the bottom of the base is pushed into the base, and the slider is lowered against the resilient force of the first resilient body. At this time, the locking means temporarily locks the slider in a lowered state of the slider. Next, the bottom wires are engaged with wire engagement portions of the heavy load, and then the rings at the ends of the bottom wires are fitted onto the mast through the T-shaped holes, respectively. The heavy load in this state is hoisted by the crane and unloaded at a predetermined place, and the locked slider is unlocked by the unlocking means, so that the slider is pushed up to the top of the mast by the resilient force of the first resilient body and thus the rings of the bottom wires are removed from the mast. When the base in this state is lifted by the crane, the bottom wires are removed from the wire engagement portions of the heavy load and released from the heavy load. In this way, the bottom wires can be dismounted from the heavy load by a simple operation, thereby enabling remarkable labor saving.
In the dismounting device for a heavy load hoisting member shown in the above JP-A-7-25578, it is required to create a plurality of kinds of devices from a small-sized one to a large-sized one correspondingly to heavy loads to be hoisted. However, since size increasing ratios of the rings of the bottom wires are larger than size increasing ratios of the devices as weights of heavy loads are increased, T-shaped holes of the plates are also required to be correspondingly increased in size, thereby causing a problem that the plates are to be increased in size than required.
Further, when the rings are increased in size and weight, it is also required to increase an elastic modulus of the first resilient body for pushing up the rings. This requires a larger force for lowering the slider, i.e., the whole of the device is configured such that the slider has a self-weight capable of being lowered against the resilient force of the first resilient body, thereby causing another problem that the weight of the device is increased than required.
It is therefore an object of the present invention to provide a dismounting device for a heavy load hoisting sling capable of ensuring a strength corresponding to a weight of a heavy load upon hoisting the same, thereby requiring only a minimally increased size of the device.
It is another object of the present invention to provide a dismounting device for a heavy load hoisting sling capable of assuredly preventing distal ends of link levers from being released from distal ends of lever holders when a heavy load is hoisted, and capable of allowing the slings to be readily and quickly dismounted from the heavy load when the heavy load is downed at a predetermined place.